Is there scripture that tells us to pray for the deceased? If so where is it and what good would this do?

There isn’t anywhere in the Bible that teaches a person can or should pray to the deceased. This idea comes from the doctrine of purgatory of the Roman Catholic church. They believe there is a place called purgatory which Catholics go to when they die in order to be “purified” before they can enter heaven. The purpose of praying for the deceased is to “lessen” the pains and/or the amount of time spent in purgatory. Once again, there is no such teaching in the Bible.